1. Field of the Invention
This invention relates to a travel assembly for a dump truck, which serves to transmit an output of its corresponding electric motor to an associated wheel by way of a reduction gear unit such that the dump truck is allowed to travel.
2. Description of the Related Art
As travel assemblies for dump trucks, there are those which transmit an output of a diesel engine to a tire wheel by using a differential and those which drive an electric motor with electric power generated by a diesel engine and transmit an output of the electric motor to a tire wheel by a reduction gear unit including a planetary gear mechanism. Dump trucks include large ones having payload capacity of greater than 100 tons and employed in mines. As travel assemblies for driving such large dump trucks, travel assemblies of the latter type tend to be adopted for the reason that their structures facilitate the availability of strength.
With reference to FIGS. 1 to 3, a description will be made about conventional travel assemblies of the latter type for a dump truck. FIG. 1 is a left side view of the dump truck. FIG. 2 is a rear view of the dump truck. FIG. 3 is a cross-sectional view showing a spindle and a reduction gear unit in one of the conventional travel assemblies for the dump truck.
As shown in FIGS. 1 and 2, the dump truck 1 has a chassis 2 as its main body, a vessel 3 tiltably mounted on the chassis 2, and front wheels 4 and rear wheels 5 supporting thereon the chassis 2 for traveling. The left and right, rear wheels 5 are both provided with the conventional dump-truck travel assemblies, respectively, whereby the rear wheels 5 can be driven. Numeral 8 in FIG. 2 designates electric motors in the conventional travel assemblies. The electric motors 8 are arranged with their output shafts inserted from inner sides of the respective rear wheels 5 as viewed in a transverse direction of the chassis 2.
As depicted in FIG. 3, each rear wheel 5 is comprised of a wheel 9 and tires 6, 7 mounted as double tires on the wheel 9.
Also referring to FIG. 3, the conventional travel assembly also has, in addition to the above-described wheel 9, a spindle 10 non-rotatably fixed on the chassis 2 and inserted on a side of an inner periphery of the wheel 9, and two bearings 11, 12 arranged side by side in an axial direction between the wheel 9 and the spindle 10. Further, the conventional travel assembly also has the electric motor 8 arranged on a side of an axial one end of the spindle 10 and fixedly secured relative to the chassis 2, a drive shaft 13 non-rotatably connected to the output shaft (not shown) of the electric motor 8, inserted on a side of an inner periphery of the spindle 10 and extending out from an axial opposite end of the spindle 10, and a reduction gear unit 14 arranged on a side of the opposite end of the spindle 10 to transmit power from the drive shaft 13 to the wheel 9.
The reduction gear unit 14 is in a state of immersion in lube oil. The spindle 10 is provided with an oil inlet hole 10a formed to guide lube oil, which has flowed into the spindle 10, into a space surrounded by the spindle 10, the wheel 9 and the two bearings 11, 12. It is to be noted that in FIG. 3, sign “L” indicates a level of lube oil when the rear wheel 5 is in a stopped state.
For related art of this kind, reference may be had to U.S. Patent Application Publication No. 2005/0059523 (FIG. 2).
In the travel assembly, the lube oil for the reduction gear assembly may produce heat and undergo overheating by agitation resistance during travel of the dump truck. This overheating deteriorates the lubrication performance of the lube oil. This deterioration in lubrication performance may become a cause of malfunction or seizure of the reduction gear unit.